One type of power converters is designed to perform zero-voltage switching control, referred to simply as ZVS control. ZVS control performs switching of a switch or a switching element while a voltage across the switch is zero. Power converters, which are capable of performing ZVS control, aim to reduce switching loss of their switching elements to have higher efficiency accordingly. An example of these power converters is disclosed as a direct-current (DC) to direct-current converter, referred to as a DC-DC converter, in Japanese Patent Application No. 2004-129393, which is referred to as patent document 1.
The DC-DC converter disclosed in patent document 1 includes first and second main switches connected in series between input terminals of the DC-DC converter, and a smoothing inductor connected between an output terminal of the DC-DC converter and the connection point between the first and second main switches. The DC-DC converter also includes an auxiliary circuit, which is comprised of a resonance inductor and an auxiliary switch connected in series to each other. The auxiliary circuit is connected between the output terminal and the connection point between the first and second main switches in parallel to the smoothing inductor. The DC-DC converter further includes resonance capacitors connected in parallel to the respective first and second main switches.
The DC-DC converter measures an auxiliary current flowing through the auxiliary resonant circuit using a current sensor.
When the measured auxiliary current satisfies a predetermined ZVS condition, the DC-DC converter turns off the second main switch, and turns on the auxiliary switch within the period from turn-off of the second main switch to turn-on of the first main switch. This results in electrical energy being supplied from the output terminal to the resonance inductor. This causes the resonance inductor and the resonance capacitors to resonate with each other.
After lapse of predetermined dead time since the turn-off of the second main switch, the DC-DC converter turns on the first main switch while the voltage across the first main switch is kept zero. This therefore results in reliable ZVS control of the first main switch, resulting in lower switching loss of the first main switch and lower switching noise.